Clark, 24, appeared in New Haven Superior Court on Tuesday in an orange jumpsuit with his hands and legs shackled to enter the pleas and to waive his right to a probable cause hearing at which he could have challenged whether prosecutors had enough evidence to try him.

He has been jailed in lieu of $3 million bail on the murder charge. Prosecutors on Tuesday revealed that they were adding a felony murder count.

Felony murder is alleged when someone dies during the commission of a felony, such as robbery, burglary, kidnapping and sexual assault, or an attempted felony. Under Connecticut's felony murder law, prosecutors don't have to prove that a killing was intentional.

Prosecutors did not released details of the charge. Murder and felony murder each carry a sentence of 25 to 60 years in prison. Clark's attorney and the prosecutor both declined to comment.

In September 2009, Le's body was found stuffed behind a research lab wall on the day she was supposed to get married in New York. An autopsy concluded she was strangled, but the motive remains unclear.

Two days before Clark was arrested, investigators found blood "in plain view" on the kitchen floor near the entrance to his apartment, according to search warrants. The warrants do not indicate the source of the blood.

Authorities took plastic door panels and carpeting with "blood-like stains" from the car in which Clark was riding in the hours after Le's disappearance.

Police say a green-ink pen under Le's body had her blood and Clark's DNA. Police have said Clark signed into the secure building with a green pen on Sept. 8, the day Le disappeared.

They had also said DNA from Le and Clark was on a bloody sock found hidden in a ceiling.

Court papers, previously released, describe a bloody crime scene and Clark's efforts to scrub floors. Investigators say Clark tried to hide a box of cleaning wipes that later was found to have traces of Le's blood.

Clark had a scratch on his face and left arm that he said came from a cat, investigators wrote in court papers.